Ignition primary voltage and injector current

The purpose of this test is to monitor the current draw from an injector whilst observing the primary ignition trace.

How to perform the test

View connection guidance notes.

1. Connect a 10:1 attenuator to PicoScope channel A.
2. Connect channel A to the negative terminal on the ignition coil and to earth.
3. Connect a low amp clamp to PicoScope channel B.
4. Select the 20 A scale and zero the clamp before clamping around the injector supply cable.
5. Start the engine and run at idle.
6. Minimize the help page. You will see that PicoScope has displayed an example waveform and is preset to capture your waveform.
7. Start the scope to see live data.
8. With your waveforms on screen stop the scope.
9. Use the Waveform Buffer, Zoom and Measurements tools to examine your waveform.

Note 

This helpfile refers to a 10:1 attenuator. If you are using a 20:1 attenuator please adjust the Probe settings for the relevant channel. These settings can be found under the Channel Options button, then: Probe > 20:1 Attenuator.

Example waveform

Waveform notes

In this waveform we can observe the current drawn by the injector (shown in red) at the same time as monitoring the primary ignition trace (shown in blue). 

Further guidance

The main reason for evaluating these two waveforms together is to identify the cause of a non-start situation or sudden loss of power, causing the engine to stop.

If the primary trace is absent, there will be no switching of the injectors as these two circuits are timed together while the loss of the injector current signifies that a fault has occurred within the injection circuit.

The frequency of the injection trace when compared to the primary signal will differ between sequential and simultaneous injection. Sequential having one pulse per 720, while simultaneous will predominantly have two. Some simultaneous systems do however have a single pulse, but these are in the minority.

GT391